There's nothing wrong with a 600 mah pack; especially if you have a field charger.

Replacement 600 mah packs are $5 or $6 right now at Servo City
http://www.servocity.com/html/battery_blowout.html

If you want a little more, you can get a Futaba 1000 mah pack for about $15.
http://www.servocity.com/html/4_8v_1...d_battery.html

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If you crashed hard enough to damage your battery pack, you might seriously consider sending the receiver (with crystal) to Hobby Services to be checked for internal damage. Here's a link with info about sending things in.
http://www.rcuniverse.com/forum/m_1131517/tm.htm